U.S. Pat. Nos. 6,484,979 and 6,484,980 contain useful summaries of the prior art in the field of electrical box supports and the teachings of those patents as well as those referenced therein are incorporated by reference. From the prior art, it can be seen that numerous attempts have been made to find a more satisfactory bend line construction that provides a precise bend line and permits straightening and re-bending the tabs used in such products without risking breakage of the tab metal, but that heretofore no entirely satisfactory such product or associated method of manufacturing it has been achieved.
U.S. Pat. Nos. 6,484,979 and 6,484,980 represent an earlier attempt to solve some of the problems addressed by the present invention. They describe in a first embodiment two and in a second embodiment three struts that are assembled in telescoping relation to accommodate different stud spacing. A tab is provided on each of the outer ends of the support. Each line along which the tab can be bent, referred to as a bend line, is defined by a discontinuous score line in the shape of spaced-apart indentations formed in each bend line. These indentations, which only partially penetrate the thickness of the metal, are sufficiently deep to weaken the metal along the bend line to facilitate bending, straightening, and re-bending. These indentations are formed by plastic deformation of the steel as a result of application of a compressive force sufficient to deform the metal. This compressive force is applied by a male die containing V-shaped protrusions that is pressed down upon the sheet metal of the tab, which in turns rests upon a flat base. The pressure of the V-shaped protrusions upon the metal of the tab causes some of the metal to be displaced, thereby creating narrow depressions, or slotted indentations, in each location where a V-shaped protrusion contacted the metal of the tab. It has been discovered over time that although the method of forming indentations in the tab with a V-shaped protrusion, and the resulting tab, had many advantages over the then-existing prior art, nonetheless, the dies being referred to have a limited life span requiring substantial oversight and it would be desirable to further improve the life of the tool while maintaining and if possible improving upon the bend life of the tab in the field. Furthermore, it has been discovered that optimally according to prior practice, a compressive force of around five tons should be applied to appropriately form each indentation in the tab, thereby creating bend lines. By contrast, the present inventor has discovered that it would be desirable to form bend lines in such tabs using less force in order to simplify tooling requirements and extend the life of the tools.
From the foregoing description and the prior art references, it can be seen that numerous attempts have been made to find a more satisfactory bend line construction that permits bending, straightening, and re-bending without risking breakage of the tab metal prior to its final installation. Therefore, one object of the invention is to provide a further improved tab construction that, when used in connection with electrical box supports, can be applied to either a telescoping or non-telescoping type support, wherein the tab can be field bent along a well-defined bend line to accommodate boxes of different depths and when necessary, can be straightened and re-bent along the same or a different well-defined bend line without risk of breaking the metal forming the tab, and to accomplish this while maintaining a reasonably trouble-free work environment for the manufacture of the tab without continual oversight, maintenance, and tool replacement. An additional object is to design the tab and the method of making it so that less force need be applied to the die in order to create a bend line, and so that when the tab is made, a much longer tool life is achieved. A further object is to form a tab in such a way as to create indentations in the tab whose boundaries are at least partially sheared to facilitate ease of field bending. Other objects will become apparent as the description proceeds.
Prior to further describing the invention, some terms will be defined. The terms “box” and “electrical box” as used herein are intended to refer to a junction box, receptacle box, switch box, terminal box, connector box or the like as are known in the electrical trade. The term “stud” as used herein is intended to include any location to which an electrical box support can be mounted, which typically would be structural members in a building surface, including wall studs, joists, rafters, etc. The term “wall” as used herein is intended to include ceiling and floor surfaces as well as walls.
The word “score” when used with reference to the invention is used to refer to a depression, one or more of which are formed in each substantially flat metal tab by a punch and die during manufacture of a tab. The referred-to depression has a boundary, one section of which includes a substantially straight weakened and/or sheared edge (referred to hereafter as a “sheared edge”) and another section of which includes a substantially parallel edge (referred to hereafter as the “opposing shoulder”) opposite the sheared edge. As will hereafter be explained, the opposing shoulder may be less sharply defined than is the sheared edge, typically being bent, with a slightly rounded or sloping edge rather than a sharp edge. The term “score line” refers to a straight line along which the metal has been weakened and/or sheared. The above-referenced sheared edge of a score is an example of a score line. A “discontinuous score line” is a line composed of two or more aligned score lines separated by a section of metal that has not been weakened or sheared. One score includes one score line. Two scores in alignment with a non-weakened portion in between make up a “discontinuous score line.”
The term “bend line” refers both to a substantially straight line along which the tab has already been bent, and to such a line along which the tab could be bent if desired. The bend line coincides with at least one score line, which weakens the tab, thereby causing any bending forces applied to the tab to produce a bend in the weakened region along the score line. The bend line also includes at least one region that has no scores and that preferably has not otherwise been weakened, thereby giving such regions a degree of strength. A discontinous score line is a form of bend line.
The term “compressive force” refers to a force applied to at least one side of a tab so as to cause or tend to cause the two opposing sides of the tab to move closer to each other. The term “shear force” refers to a force applied so as to cause or tend to cause two adjacent parts of the same tab to slide relative to each other, in a direction generally parallel to their plane of contact or, stated differently, to slide in the direction parallel to the direction of travel of the applied force (since here, the force is applied to the tab from a uniform generally vertical direction). The term “plastic deformation” refers to deformation that is substantially permanent or nonrecoverable after release of the applied force. Other terms will be defined later as they arise in the description.